Piezoactuator and a method for producing a piezoactuator

ABSTRACT

The invention relates to a piezoactuator ( 1 ) comprising a piezoelectric body ( 4 ) and elements for pre-tensioning the piezoelectric body, consisting of a first ( 2 ) and a second ( 3 ) connecting element for transferring forces to the piezoelectric body ( 4 ). The actuator is provided with an element ( 6 ) for transferring tensile/pressure forces between the connecting elements ( 2, 3 ), said element being at least partially located in a gap ( 5 ) in the form of a bore in the piezoelectric body ( 4 ). According to the invention, the piezoactuator ( 1 ) is set to a defined working curve using the pre-tensioning elements ( 2, 3, 6 ). The piezoelectric body ( 4 ) is preferably produced by the lamination of piezoelectric layers, into which a gap is drilled after lamination and the component is subsequently sintered.

[0001] The invention relates to a piezoactuator with a piezoelectricbody and elements for pre-tensioning the piezoelectric body, saidelements consisting of a first and a second connecting element fortransferring forces to the piezoelectric body, and an element fortransferring tensile/pressure forces between the connecting elements,said element being disposed at least partially in a gap shaped in theform of a bore in the piezoelectric body. The invention relatesfurthermore to a method for producing a piezoactuator having apiezoelectric body with a gap shaped in the form of a bore.

[0002] A piezoactuator of this type and a production method of this typeare disclosed in German Patent No. 198 14 697, which describes apiezoactuator comprising a piezoceramic body fashioned in the form of acylinder, said piezoceramic body consisting of a piezoceramic multilayerwhich is helical in structure. This piezoceramic body has a centralthrough bore serving to accommodate a mechanical clamping device, bymeans of which the piezoelectric body can be braced parallel to thecylinder axis between two terminal plates serving as connecting elementsfor transferring forces to the piezoelectric body. The respectiveterminal plates are connected with one another via a bar-shapedretaining element in which it is possible for a bore for conducting acooling liquid to be provided.

[0003] In the method for producing a piezoactuator of this type, ahollow piezoceramic cylinder is initially furnished with cut surfacesrunning in the form of joined helices, into which cut surfaces electrodematerial is inserted in a subsequent process step. It is proposed as avariant of this production method that a cylinder be processed fromelectrode material, that helical cut surfaces be incorporated into thiscylinder and that these cut surfaces then be filled with piezoceramicmaterial.

[0004] The object of the invention is to create a piezoactuator with alow inherent spatial requirement, which piezoactuator will uponapplication of an electrical potential provide a precisely defineddeflection of a drive unit.

[0005] This object is achieved by the piezoactuator according to claim 1and the method according to claim 13. Further features, aspects,advantages and details of the invention will emerge from the dependentclaims, the description and the drawings. Advantages, features anddetails of the invention which are described in relation to thepiezoactuator will of course also apply to the method for producing apiezoactuator, and vice versa.

[0006] According to a first aspect of the invention, a piezoactuator ofthe type specified in the introduction is further developed in such away that this piezoactuator is set to a defined working curve using thepre-tensioning elements.

[0007] It is in this way possible, given a piezoactuator of the sametype of construction, to set this piezoactuator for differentapplications. Efficient piezoactuator modules can be created withintegrated pre-tensioning and low installation space requirements. Thedesign of the piezoactuator according to the invention makes itpossible, depending on the particular design, to implement, for example,a displacement reversal, a defined setting of a working curve as afunction of temperature, a defined setting of the absolute length of themodule as a function of temperature (or temperature compensation), aforce-displacement transformation and such like. Non-exclusive examplesof these will be explained in greater detail in the further course ofthe description.

[0008] In a development of the invention, the piezoactuator has amounting pad section which is rigidly connected with the piezoelectricbody. In this way, a piezoactuator with a servo drive which movesrelative to the mounting pad section will be created.

[0009] The piezoelectric body is advantageously designed as a monolithicpiezoceramic multilayer actuator. In this way, a piezoactuator iscreated which can be economically produced. Piezoceramic multilayeractuators generally consist of a large number of alternately arrangedceramic layers and metal internal electrodes.

[0010] Preferably at least one connecting element for transferringforces to the piezoelectric body is designed as a clamping plate. Thisenables a good transfer of forces between the connecting element and thepiezoelectric body. At high clamping forces an adequately rigidconnection of the element for transferring tensile/pressure forces withthe clamping plates can advantageously, but not exclusively, be achievedvia a welded connection. Simultaneously and/or alternatively, theclamping plates can be designed appropriately both in terms of materialand in terms of plate strength.

[0011] In a development of the invention, the element for transferringforces between the connecting elements is designed in the form of asolid profile. In this way, large forces can be transferred, adjustmentof the rigidity of the element for transferring forces enabling precisedetermination of the working point of the piezoactuator in theforce-displacement diagram.

[0012] The element for transferring forces between the connectingelements is advantageously designed in the form of a hollow profile.

[0013] In a further embodiment, a medium for cooling and/or thermostaticregulating can be provided or carried in the hollow profile. In this wayit is possible to cool or to thermostatically regulate the piezoactuatorusing a coolant conducted through the hollow profile. Cooling of thepiezoactuator is particularly suitable for highly dynamic control in thelarge-signal range. Thermostatic regulation is advantageous, forexample, when a precisely settable and reproducible deflection isrequired.

[0014] A drive element of the piezoactuator is preferably accommodatedin the hollow profile of the element for transferring forces between theconnecting elements. In this way, reversal of the displacement of thedrive unit of the piezoactuator can be achieved relative to theexpansion of the piezoelectric body in the piezoactuator.

[0015] A thermal coupling medium can advantageously be provided at leastin areas between the pre-tensioning elements and the piezoelectric body.Through thermal coupling, at least in areas, via the coupling medium,heat generation, heat injection, heat dissipation and the like can becontrolled in a targeted directed and defined manner. The thermalcoupling medium can, for example, be a plastic, a fluid or the like. Theeffectiveness of the cooling and/or thermostatic regulating, asdescribed further above, can be increased further, for example, byintroducing a thermal coupling medium between the hollow profile and thesurface of the actuator.

[0016] In a further embodiment, the thermal expansion of the elementsfor pre-tensioning the piezoelectric body matches the thermal expansionof the piezoelectric body. In this way, by purposefully matching thethermal expansion coefficients of the piezoelectric body and of thepre-tensioning elements, a defined change in the displacement of thepiezoactuator as a function of temperature is adjustably maintained.

[0017] The ceramics used for piezoactuators generally exhibit thermalexpansion coefficients which deviate greatly from commonly used metals.The thermal expansion coefficients of the elements for pre-tensioningthe piezoelectric body can, for example, through the appropriateselection of material, adaptation of the design (such as the strength,the laminate structure and the like) and the like be set so that thethermal expansion of the piezoactuator as a whole can be tailoredprecisely for the application concerned.

[0018] In a further embodiment, the rigidity of the elements forpre-tensioning the piezoelectric body can be matched to a requiredworking point of the piezoactuator in the working curve. This can beachieved, for example, though not exclusively, through appropriateselection of the material, selection of the cross-section, configurationor construction of the pre-tensioning elements or parts thereof, inparticular of the element for transferring tensile/pressure forces, as alaminate body and the like.

[0019] If, for example, a defined working curve is required in theforce/displacement diagram as a function of temperature (that is, atargeted displacement change as a function of temperature), then thiscan be achieved by selectively combining the thermal expansioncoefficients and the rigidity of the pre-tensioning elements.

[0020] The elements for pre-tensioning the piezoelectric body preferablycomprise a cup spring. In a further embodiment, the elements forpre-tensioning the piezoelectric body can comprise a helical spring. Inthis way, through targeted selection of the temper of the spring, adefined working displacement and working point of the piezoactuator canbe adjustably maintained.

[0021] It is advantageous to provide at least one further element forfrictionally connecting the first and second connecting element fortransferring forces to the piezoelectric body. In this way, solid statejoints are created on the connecting elements, which solid state jointsenable a curved working traverse of a drive unit of the piezoactuator,wherein a lever action can be utilized for the working displacement.

[0022] According to a second aspect of the invention, a method forproducing a piezoactuator, in particular a piezoactuator as describedhereinabove according to the invention, is provided, in which method apiezoelectric body is produced by laminating piezoceramic layers. A gapshaped in the form of a bore is drilled in this piezoelectric body afterlamination. After the drilling process, the piezoelectric body is thensintered. After completion of the piezoelectric body, the piezoactuatoris then pre-tensioned using elements for pre-tensioning thepiezoelectric body, said elements having a first and a second connectingelement for transferring forces to the piezoelectric body and an elementfor transferring tensile/pressure forces between the connectingelements, said element being at least partially located in a gap shapedin the form of a bore in the piezoelectric body, the piezoactuator beingset to a defined working curve using the pre-tensioning elements.

[0023] In this way, a piezoactuator is created, the piezoelectric bodyof which has a high electric flashover resistance and short-circuitstrength. At the same time, the gap in the piezoelectric body of thepiezoactuator can be produced to extremely precise dimensions. Thisproduction method also makes it possible for piezoactuators to beproduced economically in large unit numbers.

[0024] Further features and advantages of the invention are shown in thedrawings and are described hereinbelow.

[0025]FIG. 1 is a sectional view of an embodiment of a piezoactuatorwith a first and a second clamping plate;

[0026]FIGS. 2 and 3 are each sectional views of piezoactuatorspre-tensioned by means of a cup spring;

[0027]FIG. 4 is a sectional view of a piezoactuator with a joiningelement shaped in the form of a hollow profile between connectingelements for transferring forces to a piezoelectric body; and

[0028]FIGS. 5, 6 and 7 are each sectional views of piezoactuators withsolid state joints.

[0029] The piezoactuator 1 shown in FIG. 1 has a first and a secondclamping plate 2 and 3 which serve respectively as a first and secondconnecting element for transferring forces to a piezoelectric body 4.The piezoelectric body 4 is constructed as a monolithic piezoceramicmultilayer actuator and has centrally a through-hole, circular incross-section, held as a gap shaped in the form of a bore 5. In this gap5 runs a metal bar 6 serving as an element for transferring forcesbetween the clamping plate 2 and the clamping plate 3 and holding thepiezoelectric body 4. The clamping plates 2 and 3 and the metal bar 6are designed for transferring high clamping forces to the piezoelectricbody, for example, for clamping forces in the region of 850 N.

[0030] The clamping plate 3 is fixed on a mounting pad section 7, bymeans of which the piezoactuator 1 is fastened in an intended operatinglocation. The piezoactuator 1 can receive an electrical signal viaterminals for supplying an electrical potential, which terminals are notdescribed further. This electrical signal results in an expansion orcontraction of the piezoelectric body 4 corresponding to a movementindicated by the bidirectional arrows 8 and 9. Such a movement of thepiezoelectric body 4 is transferred to the clamping plate 2 whichrepresents a drive unit for a drive movement indicated by thebidirectional arrow 10.

[0031] The thermal expansion of the metal bar 6 is adapted here to thethermal expansion of the piezoelectric body 4. This action can firstlyachieve a temperature-independent working curve of the piezoactuator 1,wherein the thermal expansion of the piezoelectric body 4 compensatesfor the thermal expansion of the metal bar 6 and of the clamping plates2 and 3. However, it is also possible as an alternative to this actionto select a defined ratio of the thermal expansion of the metal bar 6and the piezoelectric body 4 such that a defined change can be achievedin the working curve of the piezoactuator 1 as a function oftemperature.

[0032] As well as through selection of the thermal expansion of themetal bar 6 and of the piezoelectric body 4, the working curve of thepiezoactuator 1 can also be fixed by adjusting the mechanical tensionloading between the clamping plates.

[0033] This can be achieved, for example, by appropriate selection ofthe geometric dimensions of the metal bar 6, the clamping plate 2, 3 andthe piezoelectric body before final assembly of the piezoactuator 1. Inorder to brace the clamping plates 2, 3 via the metal bar 6, suitablethreaded clamping units or equivalent means can, however, also beprovided in the components concerned.

[0034] In order to enable a force to be introduced evenly across theentire face of the piezoelectric body 4, the clamping plates 2 and 3 areadvantageously kept curved. Particularly large forces can be transferredbetween the metal bar 6 and the clamping plates 2 and 3 if the metal bar6 and the clamping plates 2 and 3 are connected by means of weldedjoints.

[0035] In the piezoactuator 20 shown in FIG. 2, a piezoelectric body 21which is provided with a through-hole implemented as a gap in the formof a bore 22 is held on one side by a clamping plate 23 serving as adrive unit. On the other side, the piezoelectric body 21 is connectedwith a base element 25 shaped in the form of a hollow profile, whichbase element is fixed on a mounting pad section 26.

[0036] The piezoelectric body 21 is braced between the clamping plate 23and the base element 25 in the form of a hollow profile by the force ofa cup spring 27, the spring tension of which is transferred through ametal bar 28. By selecting the tensional force of the cup spring 27appropriately, it is possible to set any required working curve of thepiezoactuator 20 based on suitable pre-tensioning of the piezoelectricbody 21.

[0037] Applying a voltage to the piezoelectric body 21 via electricalterminals not described further causes an expansion or contractionmovement of the piezoelectric body corresponding to the movementindicated by the bidirectional arrows 29. This expansion or contractionof the piezoelectric body 21 is transferred to the clamping plate 23serving as a drive unit, which clamping plate then moves in accordancewith the bidirectional arrow 24.

[0038] The thermal expansion of the metal bar 28, of the cup spring 27and of the piezoelectric body 21 are in turn advantageously matched toone another.

[0039] Through appropriate selection of the spring temper of the cupspring 27 and the specification of an appropriate pre-tensioning forcefor the piezoelectric body 21 it is possible, as in the piezoactuator 1described by FIG. 1, to set a defined working curve.

[0040] In place of the cup spring 27, a helical spring or anothersuitable spring element can also be used.

[0041] The functional principle of the piezoactuator 30 shown in FIG. 3corresponds in principle to that of piezoactuator 20 from FIG. 2.However, the piezoactuator 30 has a cup spring 31 in order to brace apiezoelectric body 32 having a through-hole shaped as a gap in the formof a bore 33 between a clamping plate 34 and a mounting pad section 35via a metal bar 36. A working opening 37 is provided in the mounting padsection 35, through which opening the metal bar 36 juts so as toinitiate in a drive unit 38 a drive movement running in accordance withthe bidirectional arrow 39. The direction of this drive movement is thereversal of the displacement relative to the piezoactuator shown in FIG.2, that is, when the piezoelectric body 32 expands, the drive area movestoward the mounting pad section 35, and when the piezoelectric bodycontracts, the drive area moves by contrast away from this mounting padsection.

[0042] In contrast with this, an expansion of the piezoelectric body 21in piezoactuator 21 from FIG. 2 produces a displacement movement whichguides the clamping plate 23 serving as a drive mechanism away from themounting pad section, and produces conversely, when the piezoelectricbody 21 contracts, a movement in the direction of the mounting padsection 26.

[0043] It should be noted that, like the piezoactuator 20 from FIG. 2,the piezoactuator 30 shown in FIG. 3 can also be constructed withhelical springs or another suitable spring element in place of a cupspring. As in the case of the piezoactuators shown in FIG. 1 and FIG. 2,the thermal expansion of the components of the piezoactuator 30 are inturn advantageously matched to one another in order either to enable atemperature-independent working curve of the piezoactuator or to createa piezoactuator the working curve of which changes in a defined way as afunction of temperature. Furthermore, in conformity with the remarks inrelation to FIGS. 1 and 2, the working curve of the piezoactuator can beset in a defined way through appropriate pre-tensioning of thepiezoelectric body 32 using the clamping plate 34, the mounting padsection 35, the cup spring 31 and the metal bar 36.

[0044]FIG. 4 shows a piezoactuator 40 with a piezoelectric body 41which, in turn, has a through-hole implemented as a gap shaped in theform of a bore 42 and is braced between a first clamping plate 43 and asecond clamping plate 44 with a bar implemented in the form of a hollowprofile. The piezoelectric body 41 is fixed with the second clampingplate 44 on a mounting pad section 47 furnished with a through opening46. A drive rod 48 is provided in the piezoactuator 40 as a drive unit,which drive rod runs in the bar held in the form of a hollow profile 45,juts through the through opening 46 in the mounting pad section 47 andis fixed in the area of the first clamping plate 43. When there is adefined expansion or contraction of the piezoelectric body 41corresponding to a movement indicated by means of the bidirectionalarrows 49, a drive movement of the drive rod 48 is generated toward themounting pad section 47 or away from the mounting pad section inaccordance with the bidirectional arrow 49 a.

[0045] In order to counteract any rise in temperature of thepiezoactuator 40 during operation, there can be provision forintroducing a cooling fluid in the hollow-profile form of the bar 45.The temperature of the piezoactuator is then preferably regulated so asto enable precisely definable and reproducible deflections even forhighly dynamic control in the large-signal range.

[0046] As in the case of the piezoactuator shown in FIG. 3, however, areversal of the displacement of the drive unit of piezoactuator 40 bycomparison with the drive units of the piezoactuators from FIGS. 1 and 2is achieved.

[0047] As far as the selection of the thermal expansion of thecomponents used and the mechanical pre-tensioning of the piezoelectricbody 41 are concerned, the explanations relating to FIGS. 1 to 3 shouldbe referred to.

[0048]FIG. 5 shows a piezoactuator 50 which, like the piezoactuatordescribed previously, has a piezoelectric body 51 with a through-holewhich is held as a gap shaped in the form of a bore 52. Thepiezoelectric body 51 is braced between a first clamping plate 53 and asecond clamping plate 54 via a bar 55 and is fixed on a mounting padsection 56. In addition, the first clamping plate 53 and the secondclamping plate 54 are connected via a connecting arm 57 which acts as asolid state joint in areas 58 and 59. When an electrical voltage isapplied to the piezoactuator 50 via electrical terminals which are notdescribed further, a contraction or expansion of the piezoelectric body51 is generated, which contraction or expansion proceeds asymmetrically,however, because of the solid state joints in areas 58 and 59 so that inthe first clamping plate 53 serving as a drive unit a drive movementdescribing the form of an arc is produced, as indicated by means of thebidirectional arrow 59 c.

[0049] As far as the selection of the thermal expansion of thecomponents used and the mechanical pre-tensioning of the piezoelectricbody 41 are concerned, the explanations relating to FIGS. 1 to 3 shouldbe referred to.

[0050] The piezoactuator 60 in FIG. 6 contains a piezoelectric body 61which is mechanically braced by means of a first clamping plate 62, asecond clamping plate 63 and by means of connecting arms 64 and 65running outside the piezoelectric body 61 and forming solid state joints66 a, 66 b, 66 c and 66 d.

[0051] The piezoelectric body 61 is fixed on a mounting pad section 67via the second clamping plate 63. In piezoactuator 60 there is provideda bar 68 which runs in a gap in the form of a bore fashioned as athrough-hole 69 in the piezoelectric body 61 and provides a drivemovement in an area 69 a serving as a drive unit. When an electricalpotential is applied to the piezoactuator 60, an uneven expansioncorresponding to arrows 69 c, 69 d, 69 e and 69 f is generated onaccount of the clamping of the piezoelectric body 61 between the firstclamping plate 62 and the second clamping plate 63, which unevenexpansion produces an arching of the first clamping plate 62. Thisresults in a movement of the bar 68 in the area 69 a in a manner asindicated by the bidirectional arrow 69 b.

[0052] A lever action of the selected first clamping plate 62 on thearea 69 a is thus exploited for the movement of the area 69 a serving asa drive unit. This lever action enables a transformation of theexpansion or contraction movement of the piezoelectric body 61, i.e. thedisplacement of the area 69 a serving as a drive unit is increasedrelative to the displacement of the expansion or contraction movement ofthe piezoelectric body 61.

[0053] As far as the selection of the thermal expansion of thecomponents used and the mechanical pre-tensioning of the piezoelectricbody are concerned, the explanations relating to FIGS. 1 to 3 should bereferred to.

[0054]FIG. 7 shows a piezoactuator 70, the method of operation of whichmatches that of piezoactuator 60 from FIG. 6. The piezoactuator 70contains a piezoelectric body 71 which is enclosed and braced between afirst clamping plate 72 and a second clamping plate 73 via lateralclamping arms 74 and 75, forming solid state joints 76 a, 76 b, 76 c and76 d. In areas 77 and 78, the piezoelectric body 71 is held by aconnecting cover shaped in the form of a ring, the connecting coverbeing trapezoidal in cross-section, so as to ensure that, when thesurface of the connecting cover in contact with the first clamping plate72 is only limited, the clamping force passes symmetrically to thepiezoelectric body 71. In the piezoelectric body 71 there is provided agap 79 a held as a through-hole shaped in the form of a bore, which gapaccommodates a bar 79 b serving as a drive unit. If an electricalvoltage signal is applied to the piezoactuator 70 via electricalterminals not shown further causing an expansion or contraction of thepiezoelectric body 71, as indicated by the bidirectional arrows 79 e and79 f, relative to the mounting pad section 79 g, then the bar 79 bexecutes a drive movement, indicated by the bidirectional arrow 79 d, inan area 79 c.

[0055] As far as the selection of the thermal expansion of thecomponents used and the mechanical pre-tensioning of the piezoelectricbody are concerned, the explanations relating to FIGS. 1 to 3 should bereferred to.

[0056] It is of course possible to modify the drive concept of thepiezoactuators from FIGS. 6 and 7 to the effect that a drive occurs witha reversal of displacement relative to the expansion and contraction ofthe piezoelectric body, as has been explained for piezoactuators 30 and40 using FIGS. 3 and 4.

[0057] The piezoelectric body of the piezoactuators shown in FIGS. 1 to7 can be implemented in cylindrical form but can also be fashioned intrapezoid form, cuboid form or with an ellipsoidal cross-section.Instead of keeping the through-hole passing through the piezoelectricbody circular, it is also possible to provide a cross-section in theform of a rectangle, for example a square cross-section. In general, thetensioning of the piezoelectric body is selected such that thepiezoactuator has a working curve which is favorable for its use. Theelastic and thermoelastic properties of the material used, in particularof the piezoelectric bodies and the clamping devices are matched to oneanother for this purpose.

[0058] By providing cooling means for a piezoactuator, it is possiblevirtually to exclude temperature effects on any drive movement provided.Particularly precise drive movements can be achieved with apiezoactuator which is operated at a regulated temperature.

[0059] The piezoelectric body in the piezoactuators shown in FIGS. 1 to7 can be implemented as a sintered ceramic, the gap in it in the form ofa bore being created by means of drilling. There is always the risk herethat insulating layers located on the piezoelectric body will be damagedin the area of the clamping plates, which damage can not least resultalso in an inhomogeneous distribution of the clamping forces. It mustalso be expected that in the drilling process in the area of the gapshaped in the form of a bore material from internal electrodes locatedthere will be smeared solidly over the interior surface of the bore.This can lead in subsequent electrical operation of the piezoelectricbody to the occurrence of flashovers and short circuits.

[0060] If, by contrast, multilayer components are used as piezoelectricbodies, then because of their low resistance to delamination cracks, lowfeedrates must be operated at when they are being processed, and thereis the risk that if rinsing water and boring dust is inadequatelyremoved, excess mechanical tensions will occur leading to destruction ofthe component through cracking.

[0061] It is, however, advantageous to produce the piezoelectric body inthe piezoactuator shown in FIGS. 1 to 7 from a piezostack which is stillin a green state, i.e. is mechanically processed immediately afterlamination of the stack. The through boring in the respectivepiezoelectric bodies can be carried out using normal twist drills, withcooling and lubrication of the drill being unnecessary because thematerial is still soft. Because of the softness of the material thepressure on the drill required to achieve an adequate feedrate can alsobe kept low. If, in addition, drilling base plates are used in thedrilling process, no chipping will occur. While the drilling processalso produces in these piezoelectric bodies smearing of metal internalelectrodes which can be implemented, for example, as internal Ag/Pdelectrodes, in subsequent sintering of the component these smears,particularly the silver constituent, diffuse into the component and areeliminated with the formation of an as-fired sintered surface. Thesintered component can then be processed further without any requirementfor post-processing in the area of the through-hole. This then providesadequate flashover resistance and short-circuit strength in this areadirectly. Instead of producing the through-hole using a drill, there isin principle also the possibility of processing the raw piezoelectricbody using turning, milling and similar methods. This green processingmethod enables in particular, the efficient production of very largeunit numbers of blanks of a piezoelectric body which is outstandinglysuitable for use in a piezoactuator as shown in FIGS. 1 to 7.

1. A piezoactuator (1, 20, 30, 40, 50, 60, 70) with a piezoelectric body(4, 21, 32, 41, 51, 61, 71); and with elements (2, 3, 6, 23, 25, 27, 28,31, 34, 36, 43, 44, 45, 53, 54, 55, 62, 63, 64, 65, 72, 73, 74, 75) forpre-tensioning the piezoelectric body, comprising a first (2, 23, 34,43, 53, 62, 72) and a second (3, 25, 35, 44, 54, 63, 73) connectingelement for transferring forces to the piezoelectric body (4, 21, 32,41, 51, 61, 71); and with an element (6, 28, 36, 45, 55, 68, 79 b) fortransferring tensile/pressure forces between the connecting elements,said element being at least partially disposed in a gap shaped in theform of a bore (5, 22, 33, 42, 52, 69, 79 a) in the piezoelectric body,characterized in that the piezoactuator is set via the elements forpre-tensioning to a defined working curve.
 2. A piezoactuator accordingto claim 1, characterized in that the piezoactuator has a mounting padsection (7, 26, 35, 47, 56) with which the piezoelectric body (4, 21,32, 41, 51, 61, 71) is rigidly connected.
 3. A piezoactuator accordingto claim 1 or 2, characterized in that the piezoelectric body (4, 21,32, 41, 51, 61, 71) is constructed as a monolithic piezoceramicmultilayer actuator.
 4. A piezoactuator according to one of the claims 1to 3, characterized in that at least one connecting element fortransferring forces to the piezoelectric body (4, 21, 32, 41, 51, 61,71) is constructed as a clamping plate (2, 23, 34, 43, 53, 62, 72).
 5. Apiezoactuator according to one of the claims 1 to 4, characterized inthat the element (6, 28, 36,55) for transferring forces between theconnecting elements is constructed in the form of a solid profile.
 6. Apiezoactuator according to one of the claims 1 to 4, characterized inthat the element for transferring forces between the connecting elementsis constructed in the form of a hollow profile (45).
 7. A piezoactuatoraccording to claim 6, characterized in that a medium for cooling and/orthermostatic regulating is provided or is carried in the hollow-profileform (45).
 8. A piezoactuator according to claim 6 or 7, characterizedin that a drive element (48) of the piezoactuator (40) is accommodatedin the hollow-profile form (45) of the element for transferring forcesbetween the connecting elements.
 9. A piezoactuator according to one ofthe claims 1 to 8, characterized in that a thermal coupling medium isprovided at least in areas between the pre-tensioning elements (2, 3, 6,23, 25, 27, 28, 31, 34, 36, 43, 44, 45, 53, 54, 55, 62, 63, 64, 65, 72,73, 74, 75) and the piezoelectric body (4, 21, 32, 41, 51, 61, 71). 10.A piezoactuator according to one of the claims 1 to 9, characterized inthat the thermal expansion of the elements for pre-tensioning (2, 3, 6,23, 25, 27, 28, 31, 34, 36, 43, 44, 45, 53, 54, 55, 62, 63, 64, 65, 72,73, 74, 75) the piezoelectric body (4, 21, 32, 41, 51, 61, 71)corresponds to the thermal expansion of the piezoelectric body.
 11. Apiezoactuator according to one of the claims 1 to 10, characterized inthat the rigidity of the elements for pre-tensioning (2, 3, 6, 23, 25,27, 28, 31, 34, 36, 43, 44, 45, 53, 54, 55, 62, 63, 64, 65, 72, 73, 74,75) the piezoelectric body (4, 21, 32, 41, 51, 61, 71) is matched to arequired working point of the piezoactuator in the working curve.
 12. Apiezoactuator according to one of the claims 1 to 11, characterized inthat the elements (23, 25, 27, 28, 31, 34, 36) for pre-tensioning thepiezoelectric body (21, 32) comprise a cup spring (27, 31).
 13. Apiezoactuator according to one of the claims 1 to 12, characterized inthat the elements for pre-tensioning the piezoelectric body comprise ahelical spring.
 14. A piezoactuator according to one of the claims 1 to13, characterized in that there is provided at least one further element(57, 64, 65, 74, 75) for frictionally connecting in the first (53, 62,72) and second (54, 63, 73) connecting element for transferring forcesto the piezoelectric body (51, 61, 71).
 15. A method for producing apiezoactuator (1, 20, 30, 40, 50, 60, 70), in particular a piezoactuatoraccording to one of the claims 1 to 12, having a piezoelectric body (4,21, 32, 41, 51, 61, 71) with a gap shaped in the form of a bore (5, 22,33, 42, 52, 69, 79 a), wherein a piezoelectric body (4, 21, 32, 41, 51,61, 71) is produced by the lamination of piezoceramic layers, the gap(5, 22, 33, 42, 52, 69, 79 a) is drilled in the piezoelectric body (4,21, 32, 41, 51, 61, 71) after lamination; the piezoelectric body (4, 21,32, 41, 51, 61, 71) is sintered after the drilling process; and thepiezoactuator is subsequently pre-tensioned using elements (2, 3, 6, 23,25, 27, 28, 31, 34, 36, 43, 44, 45, 53, 54, 55, 62, 63, 64, 65, 72, 73,74, 75) for pretensioning the piezoelectric body, said elements having afirst (2, 23, 34, 43, 53, 62, 72) and a second (3, 25, 35, 44, 54, 63,73) connecting element for transferring forces to the piezoelectric body(4, 21, 32, 41, 51, 61, 71) and an element (6, 28, 36, 45, 55, 68, 79 b)for transferring tensile/pressure forces between the connectingelements, said element being disposed at least partially in a gap shapedin the form of a bore (5, 22, 33, 42, 52, 69, 79 a) in the piezoelectricbody, the piezoactuator being set to a defined working curve using thepre-tensioning elements.